// Package testing provides useful mocks for an eth1 powchain
// service as needed by unit tests for the beacon node.
package testing

import (
	"context"
	"fmt"
	"math/big"
	"time"

	"github.com/ethereum/go-ethereum/accounts/abi/bind/backends"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	gethTypes "github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/rpc"
	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
	beaconstate "github.com/prysmaticlabs/prysm/beacon-chain/state"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/event"
	"github.com/prysmaticlabs/prysm/shared/trieutil"
)

// POWChain defines a properly functioning mock for the powchain service.
type POWChain struct {
	ChainFeed         *event.Feed
	LatestBlockNumber *big.Int
	HashesByHeight    map[int][]byte
	TimesByHeight     map[int]uint64
	BlockNumberByTime map[uint64]*big.Int
	Eth1Data          *ethpb.Eth1Data
	GenesisEth1Block  *big.Int
}

// GenesisTime represents a static past date - JAN 01 2000.
var GenesisTime = time.Date(2000, 1, 1, 0, 0, 0, 0, time.UTC).Unix()

// NewPOWChain creates a new mock chain with empty block info.
func NewPOWChain() *POWChain {
	return &POWChain{
		HashesByHeight:    make(map[int][]byte),
		TimesByHeight:     make(map[int]uint64),
		BlockNumberByTime: make(map[uint64]*big.Int),
	}
}

// Eth2GenesisPowchainInfo --
func (m *POWChain) Eth2GenesisPowchainInfo() (uint64, *big.Int) {
	blk := m.GenesisEth1Block
	if blk == nil {
		blk = big.NewInt(GenesisTime)
	}
	return uint64(GenesisTime), blk
}

// DepositTrie --
func (m *POWChain) DepositTrie() *trieutil.SparseMerkleTrie {
	return &trieutil.SparseMerkleTrie{}
}

// BlockExists --
func (m *POWChain) BlockExists(_ context.Context, hash common.Hash) (bool, *big.Int, error) {
	// Reverse the map of heights by hash.
	heightsByHash := make(map[[32]byte]int, len(m.HashesByHeight))
	for k, v := range m.HashesByHeight {
		h := bytesutil.ToBytes32(v)
		heightsByHash[h] = k
	}
	val, ok := heightsByHash[hash]
	if !ok {
		return false, nil, fmt.Errorf("could not fetch height for hash: %#x", hash)
	}
	return true, big.NewInt(int64(val)), nil
}

// BlockHashByHeight --
func (m *POWChain) BlockHashByHeight(_ context.Context, height *big.Int) (common.Hash, error) {
	k := int(height.Int64())
	val, ok := m.HashesByHeight[k]
	if !ok {
		return [32]byte{}, fmt.Errorf("could not fetch hash for height: %v", height)
	}
	return bytesutil.ToBytes32(val), nil
}

// BlockTimeByHeight --
func (m *POWChain) BlockTimeByHeight(_ context.Context, height *big.Int) (uint64, error) {
	h := int(height.Int64())
	return m.TimesByHeight[h], nil
}

// BlockNumberByTimestamp --
func (m *POWChain) BlockNumberByTimestamp(_ context.Context, time uint64) (*big.Int, error) {
	var chosenTime uint64
	var chosenNumber *big.Int
	for t, num := range m.BlockNumberByTime {
		if t > chosenTime && t <= time {
			chosenNumber = num
			chosenTime = t
		}
	}
	return chosenNumber, nil
}

// DepositRoot --
func (m *POWChain) DepositRoot() [32]byte {
	root := []byte("depositroot")
	return bytesutil.ToBytes32(root)
}

// ChainStartDeposits --
func (m *POWChain) ChainStartDeposits() []*ethpb.Deposit {
	return []*ethpb.Deposit{}
}

// ChainStartEth1Data --
func (m *POWChain) ChainStartEth1Data() *ethpb.Eth1Data {
	return m.Eth1Data
}

// PreGenesisState --
func (m *POWChain) PreGenesisState() *beaconstate.BeaconState {
	return &beaconstate.BeaconState{}
}

// ClearPreGenesisData --
func (m *POWChain) ClearPreGenesisData() {
	//no-op
}

// IsConnectedToETH1 --
func (m *POWChain) IsConnectedToETH1() bool {
	return true
}

// RPCClient defines the mock rpc client.
type RPCClient struct {
	Backend *backends.SimulatedBackend
}

// BatchCall --
func (r *RPCClient) BatchCall(b []rpc.BatchElem) error {
	if r.Backend == nil {
		return nil
	}

	for _, e := range b {
		num, err := hexutil.DecodeBig(e.Args[0].(string))
		if err != nil {
			return err
		}
		h, err := r.Backend.HeaderByNumber(context.Background(), num)
		if err != nil {
			return err
		}
		*e.Result.(*gethTypes.Header) = *h

	}
	return nil
}

// InsertBlock adds provided block info into the chain.
func (m *POWChain) InsertBlock(height int, time uint64, hash []byte) *POWChain {
	m.HashesByHeight[height] = hash
	m.TimesByHeight[height] = time
	m.BlockNumberByTime[time] = big.NewInt(int64(height))
	return m
}

// BlockExistsWithCache --
func (m *POWChain) BlockExistsWithCache(ctx context.Context, hash common.Hash) (bool, *big.Int, error) {
	return m.BlockExists(ctx, hash)
}
